TracerProvider: Make format settable.

[Oberon00]

Resolves #718.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@c802811). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #914   +/-   ##
=========================================
  Coverage          ?   82.74%           
  Complexity        ?      841           
=========================================
  Files             ?      113           
  Lines             ?     2968           
  Branches          ?      252           
=========================================
  Hits              ?     2456           
  Misses            ?      399           
  Partials          ?      113

Impacted Files	Coverage Δ	Complexity Δ
...ntelemetry/trace/propagation/HttpTraceContext.java	94.66% <100%> (ø)	17 <1> (?)
...elemetry/trace/propagation/BinaryTraceContext.java	100% <100%> (ø)	13 <1> (?)
...ain/java/io/opentelemetry/sdk/trace/TracerSdk.java	100% <100%> (ø)	8 <2> (?)
.../io/opentelemetry/sdk/trace/TracerSdkProvider.java	100% <100%> (ø)	10 <1> (?)
.../io/opentelemetry/sdk/trace/TracerSharedState.java	94.11% <100%> (ø)	12 <2> (?)

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[carlosalberto]

I don't think we want this feature anymore - based on OTEP 66, now the default Propagators will be set by the API, and the user will be able to override them (removing the instances from both Tracer and CorrelationContext).

[Oberon00]

Hi @carlosalberto, I know this feature is mostly obsoleted by OTEP 66, but it seems that it will take some time until this is implemented, so I wanted to provide this PR as a remedy in the meantime. I do think, however, that we'd want to have the propagators configurable via the builder even after OTEP 66 has landed in java.

[carlosalberto]

So we really need OTEP 66 changes for the beta (March 16th). As mentioned in the related PR, now that I have my hands a little free-r, we should be able to keep that feature ready/merged relatively soon (I hope we get most of the things done/ready this week TBH).

I'd put a "Holding on" on this issue while we work on that one, and decide to apply this if for some reason we can't get it merged in 1-2 weeks.

[bogdandrutu]

@Oberon00 is this obsolete now?

[Oberon00]

I'm not sure. How would you set a custom text format with the new API? I'll look it up.

[Oberon00]

That is to say, this PR is certainly obsolete now, but I'll need to check if #718 can be closed.